The invention relates to an electronic component and a semiconductor device, a method of making the same and method of mounting the same, a circuit board, and an electronic instrument, and in particular relates to a compact electronic component and a semiconductor device having a package size close to the chip size, a method of making the same and method of mounting the same, a circuit board, and an electronic instrument.
To pursue high-density mounting in semiconductor devices, bare chip mounting is the ideal. However, for bare chips, quality control and handling are difficult. In answer to this, CSP (chip scale package), or packages whose size is close to that of the chip, have been developed.
Of the forms of CSP semiconductor device developed, one form has a flexible substrate provided, patterned on the active surface of the semiconductor chip, and on this flexible substrate are formed a plurality of external electrodes. It is also known to inject a resin between the active surface of the semiconductor chip and the flexible substrate, in order to absorb the thermal stress. In Japanese Patent Application Laid-Open No. 7-297236, as the flexible substrate is described the use of a film carrier tape.
In these methods of fabricating a semiconductor device, a semiconductor chip is cut from a wafer, and individual semiconductor chips are mounted on a flexible substrate. As a result, not only is the patterned flexible substrate necessary, but also a process is required to mount each individual semiconductor chip on the flexible substrate, and therefore the devices used in each of the steps of the process must be special-purpose equipments, and the cost is increased.
Besides, a semiconductor device to which a CSP type package is applied is surface-mounted, and has a plurality of bumps for mounting on a circuit board. The surface on which these bumps are formed is preferably protected by the provision, for example, of a photosensitive resin.
However, since a photosensitive resin is electrically insulating, and mounting while it remains on the bumps is not possible, it is necessary to remove the photosensitive resin from the top of the bumps. Here, in order to remove a part of the photosensitive resin, lithography must be applied, and this results in the problem of an increased number of steps.
In this way, a conventional semiconductor device suffers from inferior efficiency in the process from fabrication to mounting.
The invention has as its object the solution of the above described problems, and this object subsists in the provision of an electronic component and a semiconductor device, a method of making the same and method of mounting the same, a circuit board, and an electronic instrument such that the process from fabrication to mounting can be carried out efficiently.
The method of making a semiconductor device of the invention comprises:
a step of providing a wafer on which are formed electrodes;
a step of providing a stress relieving layer on the wafer in such a way as to avoid at least a part of the electrodes;
a step of forming wiring over the stress relieving layer from the electrodes;
a step of forming external electrodes connected to the wiring above the stress relieving layer; and
a step of cutting the wafer into individual pieces.
According to the invention, the stress relieving layer is formed on the wafer, and further thereon the wiring and external electrodes are laminated, so that the fabrication process proceeds as far as forming the semiconductor package while still in the wafer stage; this obviates the need for a substrate such as a patterned film with preformed external electrodes.
Here, the stress relieving layer refers to a layer which relieves the stress caused by distortion between the motherboard (mounting board) and semiconductor chip. For example, such stresses may be generated when the semiconductor device is mounted on the mounting board and when subsequently heat is applied. As the stress relieving layer is selected a material which is flexible or a gel material.
Besides, since the wiring between the electrodes and the external electrodes can be formed freely according to the requirements of the design, the layout of the external electrodes can be determined regardless of the layout of the electrodes. As a result, without changing the circuit design of the elements formed on the wafer, various semiconductor devices with the external electrodes in different positions can easily be fabricated.
Furthermore, according to the invention, after the stress relieving layer, wiring and external electrodes are formed on the wafer, the wafer is cut, to obtain individual semiconductor devices. As a result, the formation of the stress relieving layer, wiring and external electrodes on a large number of semiconductor devices can be carried out simultaneously, which is preferable when quantity production is considered.
As the stress relieving layer is used, for example, a resin with a Young""s modulus of not more than 1xc3x971010 Pa.
In the step of providing the stress relieving layer, a photosensitive resin may be applied to the wafer in such as way as to include the electrodes, and the photosensitive resin may be removed from the region corresponding to the electrodes, whereby the stress relieving layer may be provided.
The stress relieving layer may be provided by printing the resin constituting the stress relieving layer.
The photosensitive resin may be selected from the set consisting of polyimide resin, silicone resin, and epoxy resin.
The stress relieving layer may have a plate with holes formed corresponding to the electrodes adhered to the wafer; and the plate may have a coefficient of thermal expansion intermediate between those of the semiconductor chip and a circuit board on which the semiconductor chip is mounted.
By this means, since the coefficient of thermal expansion of the plate is intermediate between the coefficient of thermal expansion of the semiconductor chip and the coefficient of thermal expansion of the board, stress generated by differences in the coefficient of thermal expansion values can be absorbed. Besides, since the plate used here simply has holes formed therein, its formation is simpler than that of a patterned substrate.
The stress relieving layer may be formed of a resin in a plate form, and the plate form of resin may be adhered to the wafer.
By this means, in contradistinction to a patterned substrate, the required form can be formed easily.
The wafer used in the step of providing the wafer may have formed an insulating film, except in the regions of the electrodes and the region cut in the step of cutting.
Before the step of forming wiring, there may further be a step of roughening the surface of the stress relieving layer.
After the step of forming external electrodes and before the step of cutting, there may further be a step of applying a photosensitive resin to form a film on the surface of formation of the external electrodes to include the external electrodes, and a step of carrying out isotropic etching with respect to the photosensitive resin until the external electrodes are exposed.
After the step of forming external electrodes and before the step of cutting, there may further be a step of applying an organic film to form a film on the surface of formation of the external electrodes to include the external electrodes.
As the organic film may be used a flux such that when heated the residue is changed by a chemical reaction into a thermoplastic polymer resin.
The wiring may be bent over the stress relieving layer.
At the junction of the wiring and the electrodes, the width of the wiring may be greater than the width of the electrodes.
In the invention, the stress relieving layer may be formed, and over the stress relieving layer the wiring may be formed, and thereafter a solder portion may be formed by electroless plating, and the solder portion may be formed into the external electrodes.
In the invention there may further be:
a step in which the stress relieving layer is formed and a conducting layer is formed on the stress relieving layer; a step in which a solder portion is formed over the conducting layer by electroplating; a step of forming the conducting layer into the wiring; and a step of forming the solder portion into the external electrodes.
In the invention there may further be:
a step in which a protective film is formed over the wiring in a region avoiding the external electrodes.
The solder portion may be formed on a previously formed seat on the wiring.
The solder portion may be formed on a solder film formed by a plating process.
In the invention there may further be:
a step in which after the step of forming the wiring a protective film is formed on the wiring; a step in which before the step of forming external electrodes in at least a part of the region of the protective film corresponding to the external electrodes openings are formed; and in the step of forming external electrodes, a solder cream may be printed in the openings and a wet-back process may be carried out, whereby the external electrodes are formed.
In the invention there may further be:
a step in which after the step of forming wiring, a protective film is formed on the wiring; and a step in which before the step of forming external electrodes in at least a part of the region of the protective film corresponding to the external electrodes openings are formed; and in the step of forming external electrodes, a flux may be applied within the openings, and thereafter on each opening a piece of solder may be mounted, whereby the external electrodes are formed.
The protective film may be formed of a photosensitive resin, and the openings may be formed by a process including exposure and development steps.
In the invention, before the wafer is cut into individual pieces, there may be a step in which a protective member is provided on the surface of the wafer opposite to the surface on which the electrodes are provided.
By this means, since the rear surface of the semiconductor device is covered by a protective film, the occurrence of damage can be prevented.
The method of making a semiconductor device of the invention comprises:
a step in which a plurality of bumps are formed on one surface of a wafer;
a step in which resin is applied to the surface until the bumps are included;
a step in which isotropic dry etching is applied to the face of the resin; and
a step in which the wafer is cut into individual pieces; and wherein the dry etching step ends after the bumps are exposed and before the surface is exposed.
According to the invention, a resin is applied to one surface of a wafer. This resin is applied over the bumps, but since the bumps project from the surface, the resin is applied more thinly over the bumps than in other regions.
Then when isotropic dry etching is applied to the resin face, since the resin is removed from all regions equally, the bumps where the resin is thinnest are exposed first. At this point the wafer surface is not yet exposed, and the dry etching is stopped at this point. In this way, a wafer can be obtained in which the bumps are exposed, but the regions other than the bumps are protected by a resin covering.
Thereafter, the wafer can be cut into individual pieces to obtain the semiconductor devices.
The method of making an electronic component of the invention comprises:
a step in which a plurality of electronic elements are integrally formed in substrate form;
a step in which a stress relieving layer is provided at least in the region where external electrodes are formed on the substrate form electronic elements;
a step in which the external electrodes are formed on the stress relieving layer; and
a step in which the substrate form electronic elements are cut into individual items.
According to the invention, since there is a stress absorbing layer, stresses caused by differential thermal expansion between the electronic component and the board on which it is mounted can be absorbed. As electronic components, for example, may be cited resistors, capacitors, coils, oscillators, filters, temperature sensors, thermistors, varistors, variable resistors, fuses, and semiconductor devices.
The method of making an electronic component of the invention comprises:
a step in which a plurality of bumps are formed on a circuit board mounting surface of an electronic element;
a step in which resin is applied to the mounting surface until the bumps are included; and
a step in which isotropic dry etching is applied to the surface of the resin; and wherein the dry etching step ends after the bumps are exposed and before the mounting surface is exposed.
According to the invention, a resin is applied to the mounting surface of an electronic element. This resin is applied over the bumps, but since the bumps project from the mounting surface, the resin is applied more thinly over the bumps than in other regions.
Then when isotropic dry etching is applied to the resin surface, since the resin is removed from all regions equally, the bumps where the resin is thinnest are exposed first. At this point the mounting surface is not yet exposed, and the dry etching is stopped at this point. In this way, an electronic component can be obtained in which the mounting surface is protected by a resin covering, but avoiding the bumps.
In the invention, as the electronic element may be used a semiconductor element.
The method of making an electronic component of the invention comprises:
a step in which a plurality of bumps are formed on one surface of an electronic element board;
a step in which resin is applied to the surface until the bumps are included;
a step in which isotropic dry etching is applied to the face of the resin; and
a step in which the electronic element board is cut into individual items; and wherein the dry etching step ends after the bumps are exposed and before the mounting surface is exposed.
According to the invention, a resin is applied to one surface of an electronic element board. This resin is applied over the bumps, but since the bumps project from the surface, the resin is applied more thinly over the bumps than in other regions.
Then when isotropic dry etching is applied to the resin surface, since the resin is removed from all regions equally, the bumps where the resin is thinnest are exposed first. At this point the surface of the electronic element board is not yet exposed, and the dry etching is stopped at this point. In this way, an electronic element board can be obtained in which the bumps are exposed, but the regions other than the bumps are protected by a resin covering.
Thereafter, the electronic element board can be cut into individual pieces to obtain the semiconductor devices.
The electronic component of the invention has the external electrodes over the stress relieving layer. For example, as an electronic component may be cited a semiconductor device.
The electronic component of the invention is manufactured by the above described method, and has a plurality of bumps formed on a mounting surface, and a resin covering the mounting surface avoiding at least the upper extremities of the bumps.
The semiconductor device of the invention comprises:
a semiconductor chip having electrodes;
a stress relieving layer provided on the semiconductor chip so as to avoid at least a part of the electrodes;
wiring formed from the electrodes over the stress relieving layer; and
external electrodes formed on the wiring over the stress relieving layer.
The wiring may be formed of any selected from the group comprising aluminum, aluminum alloy, chromium, a layer of copper or gold, two layers of copper and gold, two layers of chromium and copper, two layers of chromium and gold, two layers of platinum and gold, and three layers of chromium, copper and gold.
The wiring may be formed of a chromium layer over the stress relieving layer and a layer of at least one of copper and gold.
The wiring may include a titanium layer.
Titanium has excellent moisture resistance, and therefore lead breakages due to corrosion can be prevented. Titanium also has preferred adhesion with respect to polyimide resin, and provides excellent reliability when the stress absorbing layer is formed of polyimide resin.
The wiring may have one of a layer of nickel formed over the titanium layer and two layers of platinum and gold.
In the semiconductor device, the semiconductor chip may have a protective film on the surface opposite to the surface having the electrodes.
The protective film may be of a material different from the material used for the wafer, and may have a melting point not less than the melting point of solder.
In the semiconductor device, the semiconductor chip may have a radiator on the surface opposite to the surface having the electrodes.
The semiconductor device is manufactured by the above described method, and has a plurality of bumps formed on a mounting surface, and a resin covering the mounting surface avoiding at least the upper extremities of the bumps.
The method of mounting an electronic component of the invention comprises:
a step of applying flux to a mounting surface having a plurality of bumps formed on an electronic element until the bumps are included; and a reflow step of mounting the bumps on wiring on a circuit board with the flux interposed.
According to the invention, since a flux is applied to the mounting surface, even after mounting is completed with the reflow process, the flux remains to cover and protect the mounting surface. Moreover, it is not necessary to apply the flux so as to avoid the bumps, and the application can simply be made for the whole mounting surface including the bumps, so that the application can be carried out simply.
In the invention, as the electronic element may be used a semiconductor element.
On the circuit board of the invention is mounted the above described semiconductor device.
On the circuit board of the invention is mounted the above described semiconductor device having a plurality of bumps formed on a mounting surface, and a resin covering the mounting surface avoiding at least the upper extremities of the bumps.
The electronic instrument of the invention has this circuit board.
The electronic instrument of the invention has a circuit board on which is mounted a semiconductor device having a plurality of bumps formed on a mounting surface, and a resin covering the mounting surface avoiding at least the upper extremities of the bumps.